The present invention relates to apparatus for charging or filling extractors of the type in which particularly oil-containing vegetable raw materials, such as oil seed and oil fruit, are treated with an organic solvent or extractant in a continuous process wherein the glyceride components (oils and fats) are transformed into the extracted liquid phase.
Practically the only substances used in the art as extractants or solvents for oil seeds, especially where edible oils and edible fats are to be produced, are benzene, hexane, heptane, octane or blends thereof having boiling ranges from 60.degree. to 100.degree. C.
Apparatus and equipment for continuously operating extraction processes are largely known and reference is made to the pertinent technical literature. According to the most recent developments such equipment either comprises vertically arranged extraction columns with or without agitating components or horizontally designed frame belt extractors, screw-type extractors, pot or cup-type extractors, plants including endless conveyor belts, bucket-conveyor type extractors, basket type extractors etc.
Practically all technically feasible processes operate by the countercurrent method. In accordance with this method fresh extractant is used for the final rinsing of the material having already been extracted to a high degree. This final phase of extraction is frequently preceded by several steeping, washing and extracting steps until, finally, there is obtained a miscella containing about 15 to 35% oil and 65 to 85% solvent, depending on the type of extractor used.
Subsequent to the extraction, the miscella, possibly after a blank filtering and clarification, is separated by distillation into oil and solvent. The distillation is at low temperatures with chiefly indirect steam heating and is easily accomplished in two or three stages due to the considerably different boiling points of the constituents of the mixture.
As is generally known, it is of decisive importance for the quality of a vegetable oil, such as soy oil, that the content of phosphatides (lecithin) is as low as possible.
Such phosphatides as well as the fatty constituents of the oil exhibit considerable instability against autoxidation phenomena. This is, for example, the cause of oil becoming rancid. It has long been known that edible oils will keep only for a limited time. Due to this autoxidation phenomena, with formation of unsaturated aldehydes etc., a seedlike off-flavor develops, frequently after a few weeks only.
It has now been found as a result of detailed investigation that, independent of the type of extractant or of the operating conditions during extraction, such autoxidation reactions, involving also the phosphatides, start immediately whenever the extractant comes into contact with the comminuted seed material in the presence of atmospheric oxygen or whenever free, oxidizable surfaces are formed during the comminution of the seed material.
The autoxidation of the phosphatides is due to the coaction of oxygen and certain prooxygenic substances present in the seed material, particularly enzymes.
It has already been proposed to eliminate the influence of such enzymes by subjecting the seed material to heat treatment prior to extraction. Such heat treatment does have the effect of substantially destroying the enzymes (catalases) and reducing autoxidation. However, to achieve this, considerable expenditure in the way of process technology, apparatus and energy is required, out of all proportion to the possible success that may be obtained.
The specific enzymes causing the decomposition or autoxidation of the phosphatides (lecithin) can be inactivated also by sulfur compounds. Such sulfur compounds are present in considerable measure in the raw seed material. However, these sulfur compounds become inactive when, under the action of considerable heat, particularly in an air stream, also in the presence of highly volatile solvents (hexane), reaction products of the process, in the form of H.sub.2 S, COS, mercaptanes etc., are carried away too quickly.
Summarizing, technology so far has not been in a position to stop the autoxidation of the phosphatides (lecithin) because, on the one hand, the destruction of the enzymes is not justifiable economically and, on the other hand, the coaction of enzyme and oxygen responsible for autoxidation has not been eliminated. Moreover, the working with toxic, highly flammable, low-boiling extractants, such as benzene, hexane etc. presents considerable technical problems.
Therefore, it is necessary that, under operating conditions, the mixing of the extraction feedstock with the extractant (solvent) takes place in an entirely closed system excluding any influence of atmospheric oxygen as well as the occurrence of leakages.
Especially in the extraction of vegetable raw materials, but also in other extraction processes of industrial chemistry, the extraction proper in horizontal or vertical extractors generally is preceded by comminution of the raw material, whereby the material is brought into a finely divided form (flakes) facilitating extraction.
During the comminution (flaking) of oil seeds, for example, fresh, i.e. oxidizable surfaces are exposed, whereby considerable deterioration in quality is caused even before the extraction proper.
Therefore, provision must be made to exclude the influence of oxygen (air) already directly following the flaking. That means it is necessary to ensure that the entire apparatus between the flaking device and the extractor, but especially the unit or installation for the mixing of comminuted material and extractant, forms a completely closed system permitting no access of air and no escape of solvent vapors into the atmosphere.
Further, it is well known to those skilled in the art that when flaked, i.e. comminuted raw material, meets with the extractant, overheating (spontaneous beginning of reaction or extraction) or agglomeration, agglutination etc. are apt to occur, depending on the characteristics of the material involved. These undesirable attendant phenomena, which cause considerable disturbance in the process, make it necessary to provide for an optimally adjusted mixing process of comminuted extraction feedstock and solvent.
For such mixing, generally, agitating vessels, feed screws and similar mixing apparatus are used and it is necessary to ensure proper proportioning and dosage.
It has been found that it is extremely difficult to achieve proper dosage with large quantities and in this case the above-mentioned derivative problems can hardly be mastered. In case of the intermittent admixing of small quantities the above-mentioned problems do not occur to the same extent, but such intermittent admixing of small quantities has a restrictive effect on the economical use of the installation capacity and therefore is not justifiable.